Minimally invasive surgery, or ‘key-hole’ surgery, allows for surgical devices to be inserted into a patient's body cavity through a small aperture cut. This form of surgery has become increasingly popular as it allows patients treated successfully to suffer less surgical discomfort while retaining the benefits of conventional surgery. Patients treated by such techniques are exposed to lower levels of trauma and their recovery times can be significantly reduced compared to conventional surgical procedures.
Key-hole surgery has been adopted as a favoured route for performing laparoscopic surgery as well as in a number of cardiovascular procedures. In the latter case, a balloon catheter may be used to open a partially occluded coronary artery as an alternative to open heart surgery. This technique is known as balloon angioplasty. The balloon catheter is typically a small, hollow, flexible tube that has a balloon near to its distal tip. The catheter is inserted into an artery (usually near the patient's groin) and then guided through the body to the patient's heart. The heart and cardiac arteries are visualized by using X-ray fluoroscopy, and blockages in the heart vessels are identified. A balloon catheter is then inserted in or near the blockage and inflated, thus widening the occluded blood vessel and helping to restore blood flow to the cardiac tissue.
However, balloon angioplasty is not always a suitable measure, especially in acute cases and in cases where a coronary artery is completely occluded. In these instances the typical treatment is to employ coronary bypass which involves open-heart surgery. Hence, there is a need to provide new and improved methods and apparatus for use in minimally invasive surgical procedures, such the restoration of a blood supply to ischaemic tissue.
Conventional coronary bypass surgery is not always an option for certain patients. Factors such as age, obesity, diabetes and smoking can exclude a proportion of candidate patients who are in genuine need of such treatment. In these cases it has been postulated that minimally invasive surgery could provide a means for treating a broader range of patients including those currently excluded from standard techniques. Oesterle et al (Catheterization and Cardiovascular Interventions (2003) 58: 212-218) describe a technique they call percutaneous in situ coronary venous arterialization (PICVA) which is a catheter based coronary bypass procedure. In PICVA, the occlusion in the diseased artery is ‘bypassed’ by creation of a channel between the coronary artery and the adjacent coronary vein. In this way the arterial blood is diverted into the venous system and can perfuse the cardiac tissue in a retrograde manner (retroperfusion). The technique of retroperfusion has been known for some time, having first been performed in humans by Beck in the 1940s and 1950s (for review see Keelan et al. Current Interventional Cardiology Reports (2000) 2: 11-19). Apparatus and methods for performing procedures like PICVA are described in WO-A-99/49793 and US-A-2004/0133225.
However, as the clinical results show in Oesterle et al. (supra), successfully performing a minimally invasive procedure of diverting blood flow from the coronary artery to the adjacent vein has a low success rate. In six out of the 11 cases described this was simply due to an inability to target the adjacent vein from the artery. As such, Oesterle et al's procedure is too often doomed to failure before it even starts. At present, the means for targeting the catheter consist of a combination of X-ray fluoroscopy and an imaging ultrasound probe located on the distal tip of the catheter (e.g. see US-A-2004/0133225). Indeed, such an arrangement is difficult to navigate and localisation of the adjacent vein requires considerable skill on the part of the clinician. Hence, there is a need for improvements in the means for targeting devices, such as catheters, that are used for procedures such as PICVA and in general transvascular surgery. Indeed, in the absence of such improvement it seems that such techniques will remain peripheral to the conventional surgical procedures of open-heart coronary bypass.